In the manufacturing of prestressed concrete pipe, reinforcing wire is wrapped around the pipe in a helix under tension. The wire is anchored to the pipe so as to maintain the wire in tension and the pipe in a state of compression. Prestressed concrete pipe is able to withstand much higher internal pressures as a result of the preloading effect of maintaining the wire under tension.
Various devices have heretofore been proposed for maintaining the wire under tension as it is wrapped on the outside of the pipe. One such arrangement is shown for example in U.S. Pat. No. 3,115,316. Such known systems have required multiple pump units to accommodate a wide range of tension requirements depending upon wire sizes and pipe diameters. The bull wheel around which the wire is wrapped and which controls the tension had to be mounted in a horizontal position, thus requiring expensive vertical and horizontal thrust mechanisms. Also the pumps were operated in an oil bath atmosphere requiring special oil sealing problems.